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Sports Bra Sister Size Guide

We come in all shapes and sizes and so to do our sports bras. This combination can make finding the perfect sports bra difficult. Sometimes you just can’t find the right fit, no matter how many times you measure yourself or how hard you try.

Sister Sizes to the rescue! Your usual go to size may not work for a new bra, but don’t despair, that’s what sister sizes are for!

What Are Sister Sizes?

Quite simply sister sizes are alternate sizes to your usual size where the cup volume stays the same even though the cup letters and band numbers change. Did I say it was simple?

In theory, if the cups of the bra feel correct but the band doesn’t fit quite right you can move up or down a band size whilst keeping the cup volume the same to help you find your perfect fit.

Why You Should Know Your Bra Sister Size

Not all sports bras are created equal. Add to this that we all have our own unique body shape and finding a bra that fits every time is no easy task.

If this is you, then remember it’s your bra and not you that is the problem. Knowing your sister size will give you greater success in your search for the perfect fit. Particularly if you are trying a new brand or style for the first time.

How to Find Your Sister Sizes

It’s actually quite simple (haven’t I said that before?). Starting at your regular bra size your ‘big sister’ size is simply up a band size and down a cup size. If you’re a 12D then ‘big sister’ size would be 14C.

Your ‘little sister’ size is the opposite, down a band size and up a cup size. You’re 12D would become a 10DD ‘little sister’ size.

It really is that simple. It’s all in the cup. To maintain the same cup volume the cup sizing gets smaller as the band size increases and vice versa. A 10DD, 12D & 14C all have the same cup volume even though the letters differ.

That’s the magic of the sports bra back / cup relationship.

When You Should Not Wear Sister Sizes?

Are there any occasions where you should not use sister sizes? If you’ve got a bit more up top and you need your sports bras to help keep things up. I would not recommend wearing the ‘big sister’ size, the ‘up a band size’ sister size.

Support comes from the band and there is a risk the band will be too loose and not provide the support you need. To ensure you get the support you need it is more common to go down a sister size rather than up.

The Advantage of Sister Sizes

So, you’ve spent a long time researching and searching for the perfect bra for you. It ticks all your boxes, it’s high impact, racerback, wirefree and looks perfect but it is not available in your size. Don’t despair as it is perfectly OK to check if a sister size is available. Go up one cup size and down one band size. Or down a cup size and up a band size. Try it for yourself, it almost always works!

Any Questions?

Both my band and cup don’t feel right, what do I do?

If the band and cup feel slightly loose, try going down a band size whilst keeping the cup size the same; 12D to 10D. If the band fits well but the cup still isn’t quite right, try going up or down by one cup size; try a 10C or 10DD.

If the band and cup feel slightly tight, try going up a band size whilst keeping the cup size the same; 12D to 14D. If the band fits well but the cup still isn’t quite right, try going up or down by one cup size; try a 14C or 14DD.

How do I know to go up or down a sister size?

Which sister size you select depends on how your band feels and where you fasten it. Your band should fit you comfortably on its loosest hook and eye setting.

If you’re on the tightest fastening and it still feels loose, try going down a sister size. If you’re on the loosest fastening and it feels too tight, try going up a sister size.

My sister size still doesn’t fit should I go up or down another size?

I recommend only going up or down one sister size. If the sister size still isn’t the right fit, I recommend doing a remeasure and visiting our fitting room to double check if you started with your right size. If you want further advice, please contact me I am happy to help you.

So, there you have it. A comprehensive sports bra sister size guide giving you everything you need to know to find your sister sizes and your perfect sports bra!

Yours in support.

Amy x

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With a non-padded bra on measure around your chest, directly below your bust. The tape measure should be horizontal around your body and should not drop in the back.

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